1. Field of the Invention
The present invention relates in general to organometallic source reagents for chemical vapor deposition. More particularly, it relates to thermally decomposable ruthenium and osmium organometallic compounds and complexes which are useful in chemical vapor deposition processes, for formation of ruthenium, osmium, RuO.sub.2, OSO.sub.2, and other ruthenium- or osmium-containing films on substrates. The invention also relates to a method for forming a ruthenium- or osmium-containing film by chemical vapor deposition utilizing such compounds.
2. Description of the Related Arts
Chemical vapor deposition (hereafter indicated as "CVD") is widely used for the formation of ruthenium, osmium, RuO.sub.2 and OSO.sub.2 thin films on a variety of substrates. CVD is a particularly attractive method for forming films because it is readily scaled up to production runs, and because the electronic industry has a wide experience and suitable equipment that can be applied to CVD processes.
CVD processes require suitable source reagents which are sufficiently volatile to permit a rapid transport of their vapors into the CVD reactor. The source reagents, which may be called the precursors, should be thermally stable and relatively inert against oxygen and moisture in air at room temperature to allow long-term storage. They also should decompose cleanly in the CVD reactor to deposit high purity metal component at the desired growth temperature on the substrate.
Various ruthenium organometallic complexes have been proposed as source reagents for CVD applications, which include ruthenocene and its alkyl substituted derivative complexes, such as Ru(C.sub.5 H.sub.4 Pr.sup.i).sub.2, and carbonyl complexes, such as Ru(CO).sub.4 (hfb), hfb=hexafluoro-2-butyne, [(C.sub.5 H.sub.5) Ru (CO) .sub.2 ].sub.2 and Ru.sub.3 (CO).sub.12 ; tris-.beta.-diketonate complexes, such as Ru(acac).sub.3, Ru(tfac).sub.3 and Ru(TMHD).sub.3 ; and organometallic olefin complexes, such as bis(2,4-dimethylpentadienyl)ruthenium, bis(2,4-dimethyloxapentadienyl)ruthenium, (.eta..sup.6 -C.sub.6 H.sub.6)Ru(.eta..sup.4 -C.sub.6 H.sub.8), C.sub.6 H.sub.8 =1,3-cyclohexadiene, and Ru(C.sub.3 H.sub.5).sub.2 (COD), COD=1,4-cyclooctadiene. Although some of these compounds are liquids or relatively volatile low-melting solids, which are amenable to sublimation for gas-phase transport into the CVD reactor, most of them are high-melting solids and associate with fairly high decomposition temperature, or thermally unstable and reactive towards moisture and oxygen upon exposure to air, which make them difficult to store and handle. Selected physical properties of these known organometallic reagents are listed in Table 1.
TABLE 1 Selected physical properties of known organometallic ruthenium source reagents Sublimation Condition Decomposition or Vapor Pressure Compound Melting Point (.degree. C.) Temperature (.degree. C.) (mmHg) Remarks Ruthenocene 194-198 -- vap. 85.degree. C./0.01 mm -- Ru.sub.3 (CO).sub.12 150 150 -- -- Ru(CO).sub.4 (hfb) No m.p. data -- Subl. at 25.degree. C./0.05 mm Unstable above 25.degree. C. Vap. 25.degree. C./1.5 mm Ru(acac).sub.3 .about.223 .about.220 -- -- Ru(tfac).sub.3 155-160 (2 isomers) -- -- Sublimed at 85-100.degree. C. Ru(TMHD).sub.3 200-203 250 Subl. at 120.degree. C./0.5 mm -- Ru(TMHD).sub.2 (COD) 187-190 220 subl. at 100.degree. C./0.05 mm -- Ru(C.sub.3 H.sub.5).sub.2 (COD) -- -- volatile at .gtoreq.50.degree. C. Air sensitive solid RuO.sub.4 -- -- -- Highly toxic
Accordingly, there is an urgent need for low-melting, highly volatile and relatively air and thermal stable ruthenium and osmium organometallic compounds as source reagents for various CVD applications, such as the formation of bottom electrodes, diffusion barriers, conductors, superconductors, dielectrics, capacitors, protective coating and catalytic metal alloy films. More specifically, these ruthenium source material may find applications in fabricating the four-layer RuO.sub.2 /Ru/TiN/TiSi.sub.x storage node for Gb-scale DRAM's and for manufacturing Ru pillar and Ta.sub.2 O.sub.5 /Ru capacitor in embedded DRAM technology compatible to the 0.15-.mu.m high-speed logics, whereas the osmium source reagent may find application in replacing the relatively less stable source reagent Os(CO).sub.5 for making the osmium-coated thermionic cathodes and abrasive-resistant osmium hard-coating.
It is therefore an object of the present invention to provide improved organometallic source reagents which are amenable to use in the deposition of ruthenium- and osmium-containing films.
It is another object of the present invention to provide a CVD method for forming a ruthenium- or osmium-containing film on a substrate utilizing these source reagents.
Other objects, features, and advantages will be more fully apparent from the ensuing disclosure and appended claims.